Thermostatic switch for electric discharge lamp

ABSTRACT

A THEREMOSTATIC SWITCH FOR THE ELECTRIC DISCHARGE LAMP OF SUCH A TYPE AS HAVING A HEATING FILAMENT PROVIDED ADJACENT TO ONE OF MAIN ELECTRODES AND A MOUNTING STRUCTURE OF AN ARC DISCHARGE TUBE CONSISTING OF A VERTICALLY EXTENDING METALLIC BAR TO SERVE ALSO AS LEAD-IN WIRE TO THE OTHER MAIN ELECTRODE AND AT LEAST ONE TRANSVERSELY EXTENDING METALLIC BAND MECHANICALLY AND ELECTRICALLY CONNECTED TO SAID VERTICAL BAR, SAID THERMOSTATIC SWITCH CONSISTING SUBSTANTIALLY OF A BIMETALLIC ELEMENT OF WHICH ONE END IS FIXED TO SAID TRANSVERSE BAND SO THAT THE OTHER END OF SAID BIMETALLIC ELEMENT MAY CONTACT WITH AN EXTENSION CONDUCTOR LEADING FROM ONE END OF SAID HEATING FILAMENT WHICH EXTENDS OUT OF SAID ARC DISCHARGE TUBE, THE OTHER AND OF SAID HEATING FILAMENT BEING CONNECTED TO THE OTHER MAIN ELECTRODE, WHEREBY DISCHARGE STRATING CHARACTERISTICS MAY BE STABILIZED SUBSTANTIALLY INDEPENDENT OF THE AMBIENT TEMPERATURE AND THE LAMP POSITION.

Jan. 5,1971

YOSHIO OHTAGAKI ET AL- I THERMOSTATIC SWITCH FOR ELECTRIC DISCHARGE LAMP 2 Sheets-Sheet 1 Filed Dec. 20, 1967 FIG. 2

FIG

Jan. 5, 1971 YOSHIO oI-ITAGAKI ET AL 3,553,623

THERMOSTATIC SWITCH FOR ELECTRIC DISCHARGE LAMP Filed 1380.20, 1967 2 Sheets-Sheet 2 L) i? 5O- 5 u.I V 2 4O Ii! 40 F". 30- I P 50- f2 z S 20- 1 I E 20- LB I (D T I T fi -40-2O 0 2O 4O -4O -20 O 20 4O AMBTENT TEMPERATLRE (C) AMBIENT TEMPERATURE (C) 5 Ib I5 2'0 ENERGIZING TIME IN INVERTED' POSITION I sac) United States Patent [1.8. (1337-18 3 Claims ABSTRACT OF THE DISCLOSURE A thermostatic switch for the electric discharge lamp of such a type as having a heating filament provided adjacent to one of main electrodes and a mounting structure for an arc discharge tube consisting of a vertically extending metallic bar to serve also as lead-in wire to the other main electrode and at least one transversely extending metallic band mechanically and electrically connected to said vertical bar, said thermostatic switch consisting substantially of a bimetallic element of which one end is fixed to said transverse band so that the other end of said bimetallic element may contact with an extension conductor leading from one end of said heating filament which extends out of said arc discharge tube, the other end of said heating filament being connected to the other main electrode, whereby discharge strating characteristics may be stabilized substantially independent of the ambient temperature and the lamp position.

. The present invention relates generally to a thermostatic switch provided for an electric discharge lamp and more particularly to an improvement in the position and mode of mounting the thermostatic switch in the electric discharge lamp.

High pressure mercury vapor electric discharge lamps in public use have a ballast filament connected in series withan arc discharge tube so that said filament serves as an incandescent light source for imp-roving color rendering and concurrently as a ballast means. It is rather difficult as is well known to, initiate discharge of such types of mercury lamps with the usual domestic electrical source of 100 to. 120 volts. High pressure mercury vapor. discharge lamps having an arc discharge tube in which a metallic halide such as metallic iodide is added forimproving its color rendering and efiiciency have also been in public use, which type of lamp requires relatively higher starting voltages. Even in the case of the usual high pressure mercury vapor discharge lamps, the starting voltage is fairly higher than the rate value when it is discharged in lower temperature atmospheres.

, Thus, it has been proposed for easily and sufficiently initiating discharge of the lamps, as referred to above, with the usual rated voltage to provide a heating filament adjacent to at least one of the main electrodes provided at the oppositeends of the arc discharge tube as well as a thermostatic switch to be actuated owing to self-calorificationor being heated so as to open or close the circuit for said heating filament. When initiating discharge of thelamp, said heating filament supplied, with electrical current through the normally closed thermostatic switch heats the neighboring electrode and concurrently vaporize the contained ionization medium such as a metallic halide, so as to make discharge easy between the opposite electrodes, and then said switch is thermostatically actuated to. open said circuit for the heating filament whereby discharge between the electrodes is smoothly initiated. Once discharge has been commenced, said thermostatic switch keeps said circuit open.

The thermostatic switch provided in the discharge lamp as referred to above generally comprises a bimetallic element which is mounted at a suitable portion in the outer bulb of the lamp. The position and mode of mounting such thermostatic switch is very important because behavior of said thermostatic switch is considerably affected by thermal radiation, convection, conduction and the like in the outer bulb and consequently the discharge starting characteristics may be seriously varied depending on the position and mode of mounting the switch. Furthermore, it will be noted that such position and mode have close relations to work efiiciency or steps for mounting the switch and mechanical strength of the mounting portion and other matters to be referred to hereinafter.

Two methods are generally employed for the positioning and mounting of the thermostatic switch. One is to build-in a previously assembled thermostatic switch comprising a thermostatic element such as bimetal ribbon and a pair of contacts adapted to beengaged and disengaged owing to thermostatic movement of said element, and the other is to electrically connect one end of the thermostatic element to one of the electrodes or a conductor connected thereto so that other end of the thermostatic element may contact another or contrary polarity electrode or conductor to form a thermostatic switch.

According to the former system, a bimetallic ribbon and a contact may be fixed by any desired means on a heat-resisting insulator made of glass, ceramic material or the like so as to form a complete switch of which two terminals are connected to corresponding leads or other conductors such as metallic mount members for supporting the arc discharge tube in position in the outer bulb. This structure has the advantages that the switch may be assembled separately from the mount members for supporting the, arc discharge tube and the contacting pressure of the switch may be easily regulated when manufactured. Furthermore, when it is mounted in th outer bulb of the lamp, the position for mounting may be selected at will within a relatively wide range. On the other hand it is not desirable for smaller lamps due to the increase of the number of elements to constitute the switch and that of the space to be occupied thereby.

As one example of the latter system there is a structure in which a metallic platform for supporting the arc discharge tube is fixed via insulators to a vertical metallic bar which serves concurrently as leading-in wire to one of the main electrodes of the arc discharge tube. Electrically connected to the metallic platform is a wire which leads to one end of the heating filament as well as to one end of the bimetal ribbon the other end of which in normally connected with the other end of said heating element which is in turn connected to the other main elec trode, as in US. Pat. No. 2,524,455 to Micel E. Macksoud. Such a thermostatic switch, as referred to above, may be desirable in view of the fact that it is compact. However, since the bimetallic element must be mounted in the narrower area, not only is it troublesome for mounting but also the mechanical strength of the formed switch is low. When the lamp assembly is subjected to any shock or vibration, any of the connected portions may be disengaged which causes various troubles such as misignition, short circuit etc. Furthermore, there is another defect in that the regulation of the contacting pressure is quite difficult since it must be made in relation with a-portion of the discharged tube mount assembly to be used as a contact opposite to said bimetallic element, said portion being often a vertical bar when the bimetallic element is fixed to said metallic platform or tube lead wire.

Thus, one object of the present invention is to provide a thermostatic switch. for the electric discharge lamp having a heating filament for starting which can be easily mounted in the lamp outer bulb and wherein the mechanical strength of the connected portions is considerably increased aud the contacting pressure can be easily and correctly regulated.

It is a further object of the invention to provide the thermostatic switch as referred to above, the operation of which is reliable and stable regardless of variation of the ambient temperature and the lamp position.

It is still a further object of the invention to provide the thermostatic switch as referred to above economically with use of the arc discharge tube mount structure commonly available as it is.

The above and still further objects as well as accompanying advantages will become obvious to those skilled in the art by careful reference to the description of the invention in relation to the accompanying drawings to be given merely for the purpose of the illustrations in which:

FIG. 1 is an electrical circuit diagram of an are discharge tube having a heating filament mounted therein, a thermostatic switch and a ballast filament all of which are to be contained in the outer bulb of the known high pressure mercury vapor discharge lamp,

FIG. 2 is an' elevational view of the high pressure mercury vapor discharge lamp having a circuitry as illustrated in FIG. 1 and the thermostatic switch as mounted and constructed according to the present invention,

'FIG. 3 is a perspective view on an enlarged scale of the thermostatic switch as illustrated in FIG. 2,

FIGS. 4A and 4B are graphs showing the discharge starting characteristics. of the high pressure mercury vapor discharge lamps in relation to the ambient temperature respectively provided with the known thermostatic switch and that according to the persent invention,

FIG. 5 is a graph illustrating the excellent stability of the discharge characteristics of the lamp having the thermostatic switch of this invention regardless of the lamp position, in comparaison with that having a known thermostatic switch.

Referring to the drawings, and particularly to FIG. 1, an arc tube for the high pressure mercury vapor discharge lamp is generally represented by reference numeral 1 which comprises a hollow and sealed tube 2 made of heatresistant and transparent material such as quartz glass which contains two main electrodes 3 and 4 at the opposite ends thereof and a heating filament 5 for initiating discharge at either end thereof and which is filled with lon izing medium such as mercury vapor and inert gas. This tube is the same as the usual tubes for the common hlght pressure mercury vapor discharge lamps except that 1t is provided with said heating filament 5. One end of heating filament 5 is electrically connected with electrode 4 in the illustrated embodiment while the other end is connected with a leading-in wire 6 of the arc tube via a molybdenum foil 5' embedded in the sealing portion of the tube. Electrode 4 is connected through a ballast incandescent filament 7 with one of the electric source terminals 8, while the other electrode 3 is connected with another terminal 9 of the electrical source. Main electrode 3 is connected also with leading-in wire 6 which is connected with the heating filament 5 so as to be short-circuited when a thermostatic switch 10 provided therebetween is in inoperative condition. This thermostatic switch itself is well known and located close to the arc tube, ballast filament or other exothermic means so as to operate and open the circuit owing to the radiant, conductive or connection heat produced thereby.

When a voltage is applied across terminals 8 and '9 of the electrical source, the current will flow through the closed circuit established by terminal 8, ballast filament 7, heating filament 5, thermostatic switch 10, terminal 9, whereby the filament 5 is heated, which heats also the main electrode 4 and sufiiciently evaporates the ionization medium filled in the tube 1 so that the tube may be ready for discharging between the main electrodes 3 and 4. Owing to the radiant, conductive and convection heat produced from the heated filaments 5 and 7, the thermostatic switch 10 is operated so as to open the circuit and then the main discharge is generated between the electrodes 3 and 4. After the main discharge has been commenced, the contacts of the thermostatic switch 10 are to be kept open due to the raised temperature of the radiant tube itself and of the incandescent filament 7 and thus no current flows through the heating filament 5 the temperature of which is lowered. The current will flow from the terminal 8 through the ballast incandescent filament 7, the main electrode 4, the main electrode 3 to the terminal 9. The parts circled by a dotted line in FIG. 1 are contained in an outer bulb and the thermostatic switch may be provided at various portions in various ways.

Now referring to FIG. 2 which shows the high pressure mercury vapor discharge lamp having the circuit as shown in FIG. 1 in detail, there is provided an outer bulb 11 of suitable material such as hard glass and coated at 11 on the inner surface thereof for forming a reflector. At 'the bottom of said bulb is fixed a base12 by any desired means such as cementing. The base 12 is inserted on a stem 13 protruding partly into the bulb at the bottom thereof, said stem having conductors 14 and 15 extending in the stem 13. One end of each lead-in conductors 14, 15 is respectively connected electrically to base 12 while the other end thereof extends out of the stem into the bulb. Said other end of the conductor 14 is connected with a frame work 16 for supporting the arc tube 1. The flattened end portions of the tube are respectively embraced by metallic bands 17 and 18 which are respectively fixed to said supporting frame 16. The electrode 3 is connected with said frame 16 through a conductor 19. On the lower metallic band 18 is fixed one end of a thermostatic element such as bimetal piece 20 according to the present invention. The free end of the bimetal piece 20 is adapted tocontact the leading-in wire or conductor 6 extending from the heating filament 5 contained in the tube 1. Thus the other end of the heating filament 5 can be electrically connected with the other main electrode 3 via the bimetal piece 20 and the supporting frame 16.

To the supporting frame 16 there is mounted also a heat-resisting insulator plate 21, for instance of ceramic, along which plate a plurality of anchor wires 22 are fixed so as to stretch the incandescent filament 7 thereon. One end of filament 7 is connected with the stem conductor 14 while the other end thereof is connected with the main electrode 4.

The construction and arrangement of the thermostatic ble. The contact 23 of the bimetal piece 20 may be contacted directly with the wire 6 but in order to prevent damage, fusion or the like of ,the contacting portions and assure good operation for prolonged periods it is prefera-. ble to provide an opposite contact member of silver or other high conductivity material so as to normally engage said contact 23. Said opposite contact member may take any suitable shape so as to be easily welded to said wire 6., The heating filament 5 is normally connected to the main; electrode 3 through the normally closed thermostatic switch which comprises the bimetal piece 20 arranged as referred to above.

With the construction and arrangement of the thermostatic switch as referred to above, various advantages are attained.

Firstly, it is obvious that assembling of the switchis' quite simple. It is sufficient only to fix one end'of the bimetal piece to the metallic band for supporting the arc tube so that the other end of said bimetal piece may be contacted with the lead wire for said tube. Further, the switch may be made far more compact in comparison with the usual switch.

Secondly, the mechanical strength of the mount portion of the switch may be fairly improved.

Thirdly, it is easy to adjust the contacting pressure between the contacts of the bimetal piece and the lead wire. Moreover, if the arc tube is to be fixed to the mount structure after having the middle metallic band 18 fixed thereon, the adjustment will be far easier.

Finally, since the bimetal piece of the switch may be located close to the heating filament of the arc tube, it can receive enough terminal energy through conduction and radiation to assure reliable operation substantially without being affected by the ambient temperature fluctuation. Thus the discharge starting characteristics of the lamp provided with the thermal switch according to this invention is extremely stable as shown in FIGS. 4a and 4b, in which the results were obtained with the use of a high pressure mercury vapor discharge lamp having a ballast filament of 120 v. rated input voltage and 275 w. rated electric power in the inverted position (base up position, the position of FIG. 2 being the base down position) the time of energizing the heating filament (sec.) being taken as the ordinate and the ambient temperature C.) being taken as the abscissa. FIG. 4a shows the results with one of the known thermal switches which is manufactured separately by mounting the bimetal piece on the ceramic plate as referred to at the beginning of this specification while FIG. 4b shows the results with the present invention. It is to be appreciated that the time during which the heating filament must be energized and consequently the time required until the discharge is commenced is considerably varied depending on the ambient temperature in accordance with the known switch while it is substantially constant in the present invention.

It has also been found that the function of the thermostatic switch according to this invention is hardly affected by the position thereof. This is also an important advan tage of the present invention, which is illustrated in FIG. 5 which results were obtained with use of the lamps as used in respect of FIGS. 4a and 4b. The ordinate represents the time necessary for energizing the heating filament until starting dicharge (sec.) in the usual position of the lamp i.e. that illustrated in FIG. 2 while abscissa represents said time in the inverted position. The characteristics of the known switch are represented by the dotted line while those of the present invention are represented by the solid line. It is readily appreciated that the latter solid line is close to a 45 inclination which means that the switch of this invention can be constantly actuated without being adversely affected by the position of the lamp.

It may be also pointed out as one of the advantages that this switch can be applied to the usual lamp structure without necessity of any change thereof for adopting this invention.

This invention has been explained merely for illustration as being applied to a mercury lamp having a ballast filament but it may also be applied to other types of discharge lamps such as a mercury lamp with added metallic halides. It will be necessary in this case that a ballast choke or transformer be used instead of the ballast filament.

We claim:

1. An electric discharge lamp comprising: an arc discharge tube including a pair of main electrodes located therein at respective opposite ends thereof, and a heating filament located in said tube at one end thereof adjacent one of said main electrodes, said filament having one end electrically connected with said one electrode, a lead conductor connected to the other end of said filament and passing through the tube in sealed relation; a mount structure supporting said are discharge tube and including a vertical metallic bar and a transverse metallic band holding said tube at said one end, said vertical bar and said transverse band being mechanically and electrically connected so that said mount structure serves as a conductor to the other main electrode; a bimetallic thermostatic switch adapted to electrically connect said lead conductor with said other main electrode to establish an electric circuit for heating said filament prior to ignition of said arc discharge tube and to be opened after ignition of said arc discharge tube, said bimetallic thermostatic switch including a bimetallic strip having one end fixedly inserted between the outer surface of said one end of the tube and the inner surface of said band of said mount structure adjacent said heating filament, and an opposite end facing said lead conductor to come into contact therewith, whereby the switch is operable without substantial effect by ambient temperature fluctuation.

2. A thermostatic switch as set forth in claim 1, in which said bimetallic strip is a substantially U-shaped ribbon.

3. -A thermostatic switch as set forth in claim 2, in which a shorter leg of said U-shaped bimetallic ribbon is mechanically and electrically connected to the transverse band and a contact is provided at the free end of the longer leg facing said lead conductor.

References Cited UNITED STATES PATENTS 2,278,816 4/1942 Zabel 3133 2,524,455 10/1950 Macksoud 3l311l 2,951,959 9/1960 Fraser et al 313-25 2,615,146 10/1952 Macksoud 31549X 2,491,881 12/1949 Van Liempt 315-49 2,295,657 9/ 1942 Hodgkins 315-47 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner U.S. Cl. XJR. 

